Why is it suggested that tables created by EXTRACT are used for queries instead just using the FIELDATA table directly? What exactly does the EXTRACT function do, anyway?
There’s no reason that you CAN’T use the FIELDATA table for queries; you’re certainly welcome to. However, FIELDATA field names are generic, and therefore do not adequately describe the data contained in the field: the field definition is determined by the setup of the Data Set Type (field name correlations should be documented in your DATASTYP table). (Further discussion of FIELDATA field names is available elsewhere in this FAQ.) Also-and maybe more importantly–there are many situations (e.g. if you need any mathematical operation–e.g. sum or average–ACROSS “values” [i.e. value001, value002, …valuennn], or if you must select anything based on multiple “values”) where it is MUCH simpler to use the extracted data. All the “extract” routine does is create real-world field names (e.g. “Plot” vs. “MU level 3”) and “normalize” the data (creates a single record for each “value”). It does NOT manipulate the data values in any way, shape, fashion, or (dare I say it?) “form”!
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